PROJECT SUMMARY This study will examine the specialized molecular features of the integrin ?v8 that enables activation of latent-TGF-. The activation of latent-TGF- is a critical step in the initiation of fibroinflammatory processes that occur during airway disease and other fibrotic lung diseases. There are dual long-term goals of this study. The first is to understand the structural mechanism by which integrins modulate their ligand-binding properties and the second is to acquire a deep understanding of the process of TGF- activation to develop new strategies and treatments for airway disease in COPD. Three AIMs address this goal using new technological developments in electron microscopy to study the structure of difficult to study proteins: 1) Single particle electron cryomicroscopy to determine the near atomic structure of an integrin ectodomain in the extended fully active conformation, something that has not been achieved before. We focus on the integrin ?v8 an integrin unusual in its conformational homogeneity and propensity to extend. 2) Single particle electron cryomicroscopy to determine the near atomic structure of the integrin ?v8 in complex with latent-TGF-. The complex of an integrin with latent-TGF- has not yet been solved, which is an essential step in mechanistic understanding of latent-TGF- activation, and rational design and optimization of inhibitors. 3) Single particle electron cryomicroscopy to understand the mechanistic basis of integrin allosteric regulation of ligand-binding affinity. We will use allosteric blocking and non-blocking Fab fragments to address the conformational changes associated with integrin ?v8 ligand-binding affinity. These studies will address the key question in lung fibrosis biology: What are the basic structural mechanisms underlying the initiation of signals that cause and sustain inflammation and the fibrotic responses? The successful completion of these AIMs will be transformative in integrin structural biology and allow the first atomic-level understanding of the mechanistic basis of integrin allostery in an intact integrin. We will understand the mechanistic basis of antibody inhibitors that show efficacy in preclinical models to treat airway remodeling. Structures obtained will simultaneously reveal new insights into the structural basis of integrin function, while providing the mechanisms of action of allosteric integrin inhibitors.